In this study, tension-tension fatigue tests were conducted to investigate the residual stiffness degradation of carbon fiber-reinforced polymer (CFRP) tendons. Different stress levels were used in the tests, and measurements of residual stiffness and the number of loading cycles were taken. Based on experimental data for CFRP tendons, a quantitative residual stiffness model was developed by modifying Yao's model. This model is applicable to various stress levels. To assess its accuracy and applicability, the predicted results of this model were compared with those of cited models from other researchers. The findings revealed a three-stage degradation of residual stiffness in CFRP tendons under different stress levels. Furthermore, it was observed that the proportion of fatigue life accounted for by Stage III decreased with smaller stress ranges, while the proportion accounted for by Stage II increased. The proposed quantitative residual stiffness model was verified using both experimental and cited data. Tension-tension fatigue tests of CFRP tendons were conducted at various stress levels. A quantitative model was proposed based on the residual stiffness of the CFRP tendon. Stress level influence on stiffness degradation of composite material was discussed. Model accuracy was verified against experimental and cited data.

The snow galleries along the Iron Ore railway line in northern Sweden have facedproblems in recent years due to increasingly large snow loads, and several gallerieshave been damaged. These incidents motivated an evaluation of the maximumload supported by the galleries before collapse, which is presented in this study. In2021, a monitoring system was installed in one of the main frames of two snowgalleries built in the 1950s to follow up with temperature and displacements,including a trigger that sends out a warning message when a critical load isreached. A literature review on snow loads was performed, followed bycalculations on snow distribution on the galleries based on the Eurocodes andNational Swedish Standards. Finite element 2D and 3D models were created usingAxisVM to accurately assess the efforts in the structural elements. Analysis anddiscussion are complemented by observations from site visits. It was concludedthat the critical loads supported by the galleries are lower than the requirements oftoday’s standards, but since secondary construction elements were damagedbefore the main frames reached their full capacity, no major collapse has yet takenplace. The cobweb effect (load re-distribution between the neighboring elementsin a 3D structure) influenced the behavior of the galleries in the 3D analysis and thecapacity of the main frames proved to be significantly increased compared to the2D assessment.

The direct socio-economic consequences of the deterioration of aging infrastructure systems have triggered a continuous process of revising and updating current design standards and guidelines for critical network components. Specifically, long-term degradation processes demand the analysis and evaluation of vital structural assets such as prestressed concrete bridges. It is crucial to develop theoretically consistent, user-friendly, and non-destructive methodologies that engineering professionals can employ to prevent and mitigate potential catastrophic outcomes during the service life of these bridges. This study provides a thorough review of the available testing methods employed over the years for prestressed concrete bridges and introduces a comprehensive framework for evaluating existing methods for residual prestress force assessment. Through a multi-criteria selection process, the three most feasible tests were designed and carried out on an existing 66-year-old balanced cantilever box girder bridge exposed to freezing temperatures that affected the instrumentation plan and test execution. Finally, predictive models compliant with standard codes were calibrated based on the experimental results and the life cycle loss of prestress forces was evaluated to assess relevant bounding intervals. Findings reveal limited on-site testing and discrepancies between calculated residual forces and predictions by standard codes. The saw cut method showed a 18% difference from the initial applied prestress according to the prestress protocol, suggesting the use of a cover meter and concrete modulus evaluation for improved accuracy. The strand cutting method resulted in a 14% difference, emphasizing the need for stress redistribution assessment. The second-order deflection method showed a 6% difference, indicating a focus on enhanced boundary conditions and thorough sensitivity analysis for future investigations.

The transport infrastructure consists of roads, bridges, and tunnel networks. Among these, bridges, viaducts, and tunnels are particularly vulnerable due to structural degrad-ation caused by environmental conditions, overloading, and other factors. Ensuring the safety of these assets, especially at the network level, is a significant challenge. The emergence of Bridge Management Systems (BMS) addresses the need for comprehensive information in managing inspections, condition assessments, and optimizing investments in bridge maintenance. Despite the benefits, many countries face challenges in identifying high-risk bridges. Issues include the lack of high-quality data, mixed ownership of assets, diverse management system platforms, varying condition rating schemes, and the absence of a risk-based assessment. This review aims to highlight current practices and research efforts in evaluating bridge condition indices/ratings (BCI) for existing bridges. The identified knowledge gaps emphasize the need for national authorities to develop policies leading to a unified and functional approach for condition rating.

Bridge load testing is one of the tools engineers are using for the assessment of existing bridges, which is becoming increasingly important to manage the existing bridge stock in a sustainable manner. Over the past years, various research groups have worked on theoretical and practical research regarding load testing. Moreover, various international committee work on load testing recommendations. This paper provides an overview of recent research efforts in Denmark, the Netherlands, and Sweden. The way in which recent research efforts are implemented in new committee reports and guidelines is highlighted. Overall, the efforts have focused on combining load testing with insights in structural behavior, applying improved instrumentation techniques, combining with numerical analyses, and providing a probabilistic substantiation. In conclusion: bridge load testing is a dynamic field of research that benefits from international collaboration. Further improvements to existing codes and guidelines will be forthcoming in the next years.

A bridge failure can result in significant social, economic, and environmental problems; therefore, its reliability and risk management are essential. Bridges’ system reliability and risks are governed mainly by their redundancy and robustness, which currently are not adequately included in most design code specifications. Thus, in this study, a comprehensive comparison between relevant importance, redundancy, and robustness indicators found in the literature with different levels of complexity is carried out. The indicators under analysis have been used separately in different studies but have never been addressed together. Therefore, this study presents a joint evaluation of deterministic, reliability- and risk-based indicators to evaluate the differences in interpretation and information provided by the indicators. The approach is exemplified by analyzing a prestressed concrete bridge subjected to continuous degradation due to chloride ingress. A procedure is implemented to couple a metamodel-based reliability approach with a Nonlinear Finite Element Analysis (NLFEA). Based on the analysis performed, the comparison between indicators showed how different interpretations can be obtained depending on the implemented approach. Thus, creating more uniform formulations and agreeing on target values is necessary to help with redundancy and robustness interpretation.

This document is the final report for project BBT 2020-013 (Trafikverket). It presents the results for the development and testing of a loading system based on realistic convoy loads for serviceability limit state (SLS) applied to the Kalix Bridge. It also includes a determination of the bridge condition through non-destructive testing (NDT) and assessment of non-destructive methods for the determination of residual prestressing forces. The work carried out included the development of linear and non-linear finite element models and their calibration, based on the information collected in the experimental part. Digital twin models intended for the prediction of bridge response were also created, and novel AI-based methods for crack detection were evaluated. In addition, a framework for condition management based on reliability and robustness parameters was developed within the scope of the project. As the Kalix Bridge was replaced by a new structure in 2022, the report summarizes a comprehensive review of methods for demolition of prestressed bridges and presents a methodology for demolition based on numerical analysis of the structure, considering the specific characteristics of the project and existing information about the bridge.

Railway bridges with masonry abutments represent a significant portion of aging infrastructure in north Sweden. The assessment of their structural integrity is crucial to ensure safe and efficient railway operations. This paper presents the development of a proof loading method tailored specifically for railway bridges with masonry abuments.

Before conducting the tests, the bridge condition was assessed through visual inspections using ground-based photogrammetry and Ground Penetration Radar (GPR). Realistic loads were simulated using a carefully chosen train fleet during the tests to evaluate load-carrying capacity and structural integrity. Comprehensive data, including strains, displacements, temperature, and acceleration measurements, were collected to gain insights into the bridges' behavior under real-life loading conditions. This data played a crucial role in making predictions and guiding maintenance decisions for targeted rehabilitation efforts. 

To enhance capacity assessments, finite element models were calibrated using test results, enabling predictions of how the bridges would respond to varioius loads.